<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8" />
        <meta name="viewport" content="width=device-width, initial-scale=1.0" />
        <title>Document</title>
    </head>
    <body>
        <style>
            /* 1 */
            h2 {
                color: black;
            }
            /* 11 */
            h2.hd {
                color: red;
            }
            /* 12 */
            div.main h2 {
                color: blue;
            }
            div.main h2 {
                color: yellow;
            }
        </style>
        <div class="main">
            <h2>houdunren</h2>
        </div>
    </body>
</html>
